JSCBC-132: Fixed incorrect expiry option validation.

Change-Id: I83e6583d69e63d301404b6e6fbbd83bc81db59d9
Reviewed-on: http://review.couchbase.org/40691
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Brett Lawson <brett19@gmail.com>